Cápsulas Informativas

Cápsulas Informativas

Trepidatory or oscillatory earthquakes ?

During an earthquake, the ground can vibrate vertically and horizontally, mainly due to the arrival of P and S waves radiated by the source. These movements are popularly known as "trepidatory" and "oscillatory" movements. Because the P wave is the fastest, you will first feel a vertical movement, upon the arrival of the S wave. This second wave carries the greatest amount of energy and is the one that usually causes the most damage in the epicenter zone.

Where Do Most Earthquakes Occur?

Approximately 85% of the world's seismic and volcanic activity is generated in the Ring of Fire. The chain of volcanoes that borders the Pacific Ocean, along the western coast of the American continent, from Chile to Alaska (passing through Mexico and California), and along the east coast of the Asian continent, from Alaska to New Zealand is known as the Ring of Fire. The Earth's lithosphere is composed of about 15 or more major pieces known as tectonic plates, which for many millions of years have floated on partially molten rocks. The relative movement between the plate that lies under the waters of the Pacific Ocean and the plates that surround it gives rise to the intense seismic and volcanic activity of the Ring of Fire, thus marking the boundary between these tectonic plates. The seismic region that follows the Ring of Fire is the alpine region (India, Iran, Turkey), with around 5-6% of the world's seismic activity.

The largest earthquake in history

The largest earthquake known, and instrumentally recorded, occurred on May 22, 1960 in the southern portion of Chile with a magnitude of 9.5. Even so, the Chileans had the good fortune that 30 minutes before the occurrence of this macro-earthquake, a "precursor earthquake" of lesser magnitude occurred and caused the population to go out into the streets. People from the streets observed minutes later how the earthquake destroyed their homes.

Radius proyect

In 1998 the city of Tijuana was selected by the ONU (out of 55 cities in the world) to carry out a study of Urban Seismic Risk Management. Being CICESE the scientific advisor of the study, it was possible to structure an action plan to reduce the seismic risk of this city. The project ended with an International Symposium, held in October 1999 in the city of Tijuana, which was attended by representatives of 64 cities that have already suffered earthquake damage. For more information go to the page:

Tsunami

TSUNAMI is the name given to the gigantic waves produced by earthquakes that occur below or near the oceans. These earthquakes, by causing the seafloor to move vertically, produce a violent movement of the body of water, thus generating the tsunami. Tsunamis have wavelengths between 150 and 350 kilometers and travel at speeds of around 800 km / hour. When approaching the coasts, the length of the wave decreases rapidly, while its amplitude begins to grow considerably, being able to reach up to 30 meters in height. Small earthquakes, and those that produce horizontal displacements of the seabed, do not generate this type of destructive waves. If you want to know more about tsunamis, go to the following page:

Separation of Baja California from the continent

The peninsula of Baja California is slowly separating from the rest of our continent. The peninsula is part of the Pacific tectonic plate, while the rest of Mexico is part of the North American plate. These plates move horizontally in opposite directions, such that the peninsula of Baja California travels in a northwest direction with respect to the rest of the country at an average speed of 6 centimeters per year. Although there is no strong enough reason to guarantee that this process of relative movement between plates continues for millions of years, it is believed that if the process continues, the peninsula would travel approximately 1000 kilometers in some 16 million years, placing by then the city of Ensenada in front of San Francisco, California.

seismic activity in the world

Annually several million earthquakes of various magnitudes occur throughout the world, although only the largest tremors are those that cause damage to society. Tremors of small magnitude are only detected by seismological equipment of very high sensitivity. According to statistics based on catalogs of global seismicity, on average in a year only an earthquake of magnitude 8 or greater occurs, 18 occur with magnitudes between 7 and 7.9, 120 with magnitudes between 6 and 6.9, 800 with magnitudes between 5 and 5.9 , 6,200 with magnitudes between 4 and 4.9, and 49,000 with magnitudes between 3 and 3.9. Tremors of magnitudes less than those indicated can occur by thousands during each day.

Small earthquakes keep big ones from happening

No. The energy released in events of small magnitudes is negligible compared to the energy released by large earthquakes. In the table presented below, it can be clearly seen that when passing from magnitude 4.0 to 5.0, for example, the energy changes by a factor of 32, while when passing from magnitude 4.0 to 6.0 the factor is 1000. You can see also that the seismic energy released during an earthquake of magnitude 8.0 is equivalent to the energy of about 1,000,000,000 (! billion!) of micro tremors of magnitude 2.0. After a strong earthquake occurs in a region, the deformation energy recharge cycle in the rocks starts again, and energy can accumulate faster than the energy released with the occurrence of events of small magnitude.

IS THERE ANY RELATIONSHIP BETWEEN THE OCCURRENCE OF EARTHQUAKES AND THE WEATHER?

NO. The wind, the rains and the changes of temperature affect only the terrestrial surface, whereas the earthquakes originate to several kilometers of depth. Earthquakes commonly occur during any season of the year, under any type of weather and at any time of the day.

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Fuente: Imagen cortesía de Andrea Parra.

CAN THE EARTHQUAKES BE PREDICTED?

No. The prediction of earthquakes is considered a goal of seismology. A valid prediction would have to specify with a very good precision the magnitude, date and place of occurrence of the earthquake, which has not been possible until the present. >